Airflow and Duct Sizing Flashcards
7 cards from real 313D practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Airflow and Duct Sizing flashcards as text
What is the recommended minimum clearance between a supply register and an exterior wall to prevent cold drafts in heating mode?
Answer: Register should be placed on or near the exterior wall directly
Supply registers placed on exterior walls or floor under windows offset cold infiltration and create a comfort barrier against exterior surfaces.
In a variable air volume (VAV) residential zoning system, what component modulates airflow to individual zones?
Answer: Motorized zone dampers
Motorized zone dampers open and close based on thermostat calls to deliver the correct amount of conditioned air to each zone.
When a zoning system closes multiple zone dampers simultaneously, what device prevents excessive static pressure buildup in the supply plenum?
Answer: Pressure-relief damper or bypass damper
A static pressure bypass damper or pressure-relief damper opens when supply pressure rises above a setpoint, preventing equipment damage and noise.
What is the effect of an oversized supply duct on room airflow distribution?
Answer: Reduces air velocity causing poor throw and stratification
An oversized duct lowers air velocity, reducing register throw and leaving the room with poor air mixing and temperature stratification.
Which test method uses a calibrated fan and pressure measurements to quantify duct leakage in CFM at a reference pressure of 25 Pascals?
Answer: Duct blaster pressurization test
The duct blaster test pressurizes the duct system to 25 Pascals and measures the airflow required to maintain that pressure as an indicator of leakage.
A homeowner complains that one bedroom is consistently warmer than others in cooling season. The technician measures lower-than-design CFM at that register. What is the FIRST component to inspect?
Answer: The duct run serving that room for restrictions, kinks, or disconnections
Low airflow at a specific register most commonly results from a duct restriction, kink, or disconnection in the branch serving that room.
What is the purpose of a duct transition fitting that changes from a rectangular trunk to a round branch?
Answer: To smoothly convert airflow from one duct geometry to another with minimal pressure loss
Transition fittings are designed to convert duct geometry while minimizing turbulence and pressure drop through gradual shape changes.